The Polikarpov I-16 was the last of Nikolai Polikarpov's fighter designs to enter production, and was the most important fighter aircraft in the Red Air Force by 1940. It was also the first monoplane fighter with an enclosed cockpit and retractable undercarriage to enter front line service anywhere in the world, but a lack of suitable replacement aircraft meant that it remained in production until 1941, by which time it was virtually obsolete.

Development

The first sketches of the new aircraft were produced in 1932, when Polikarpov was working as Sukhoi's deputy at Brigade No.3 of the TsKB (Central Design Bureau). This was originally the cover name for a team of designers who were working while interned, after being charged with a wide range of crimes as part of an attempt by the Secret Police to gain control of the aircraft industry. Polikarpov himself had been charged with sabotage in 1929. The TsKB designation continued to be used long after the designers had been freed. Serious work began in 1933, when Polikarpov was head of Brigade No.2.

Polikarpov wanted to build his new fighter around the 700hp Wright R-1820 Cyclone radial engine which was expected to enter licensed production in the Soviet Union. The negotiations proceeded very slowly, and so alternative engines had to be used for the two prototypes. The first received a 480hp M-22 engine, a Soviet-built version of the Bristol Jupiter VI, while the second was powered by a 600hp Wright Cyclone 1802-F-2 that Polikarpov had acquired.

The prototypes were given the designation TsKB-12 as the twelfth aircraft to be designed by the Central Design Bureau (TsKB). Work on the prototypes began in June 1933, and both were ready for their maiden flights by the end of the year.

The first prototype (M-22 engine) made its maiden flight on 30 December 1933, with skis instead of the wheeled retractable undercarriage. The Cyclone-powered second prototype made its maiden flight in January 1934. The high regard in which Polikarpov was held at this date was demonstrated in November 1933, when the Soviet Council for Labour and Defence decided to put the new aircraft into series production at zavod 21 at Gor'ky. A small number were also to be built at zavod 39, the factory attached to the design bureau.

Both prototypes took part in state trials from 16 to 27 February 1934. The first prototype reached a top speed of 190mph at sea level and 175mph at 16,400ft. The second prototype was faster, with a top speed of 215mph at sea level and 195mph at 16,400ft.

In March the first prototype underwent trials with the retractable wheeled undercarriage. This time its top speed rose to 223mph at sea level and 201mph at 16,400ft. These were good figures for 1934, and suggested that the Cyclone powered I-16 would be on a par with the best foreign fighters of the period. The standard German fighter of 1934 was the 186mph Arado Ar 65, while in Britain the Gloster Gladiator biplane made its maiden flight on 12 September 1934, and had a top speed of 236mph at 10,000ft. When the second I-16 prototype received a Cyclone F-3 engine later in 1934 its top pseed rose to 271mph.

Development was briefly held up when the second prototype was damaged in a crash, but it was rebuilt with a new cowling, the Wright Cyclone F-3 and some other minor changes and tests resumed in September 1934.

The I-16 would soon be left behind by more modern aircraft. In Germany the prototype Bf 109 made its maiden flight in September 1935. The Hawker Hurricane first flew on 6 November 1935, and its prototype reached 315mph, while the Spitfire made its debut on 5 March 1936, and had a top speed of 349mph. Production standard I-16s didn't break 300mph until the introduction of the I-16 tip 24 in 1940, and even then most standard aircraft failed to reach their full potential. The main limit would prove to be the single row radial engines used to power the aircraft. These were soon outclassed, first by the inline engines of the Spitfire or Bf 109, and then by the multi-row radial engines that powered later American fighters.

Early trials revealed that the I-16 was fast and very manoeuvrable for a monoplane, but also somewhat difficult to fly and not suitable for novices. As a result a two-seat trainer, the UTI, was ordered into production for use as a conversion trainer, and new monoplane basic trainers were eventually needed. Over time many of its bad habits were eliminated, and the later versions were considered to be rather easier to fly.

Description

The I-16 had a stocky barrel-shaped but streamlined fuselage, built around a wooden monocoque, with wooden frames, longerons and stringers and a birch plywood skin. The large tail used a duralumin frame with a fabric covering. Polikarpov chose to use a radial engine for his new fighter because the inline engines then available in the Soviet Union were heavier than their radial equivalents and only produced the same power. The extra streamlining allowed by the smaller frontal area of the inline engines didn't make up for the extra weight, and the radial engines were also better able to stand up to battle damage.

The low cantilevered wing was constructed in three sections - a central section built into the fuselage and two outer panels. The wing was built around two stainless steel spars connected by duralumin ribs and tubular struts. The outer panels were connected to the central structure by tubular fittings with threaded outer sections. The wing was fabric covered but with duralumin strips at key points, including over the join between outer and central sections and over the leading edge. The wings had no dedicated flaps, but both ailerons could be lowered at the same time, effectively performing the same role.

The prototype and early production aircraft had a fully enclosed cockpit, with a sliding canopy and a downward opening door on the port side. On many later aircraft the enclosed cockpit was removed and a windscreen replaced it. The aircraft had manually operated retractable landing gear which needed 44 revolutions of its handle to fully retract.

The I-16 was designed to be the smallest and lightest aircraft that could satisfy the demands of the Red Air Force, and was actually slightly shorter and with a narrower wingspan than the I-15 biplane. Its centre of gravity was positioned to improve manoeuvrability, although this did reduce its stability in flight, and at first it was considered to be a difficult aircraft to fly, only suitable for experienced pilots.

The prototype was originally unarmed, but later gained two wing-mounted 7.62mm machine guns, the standard armament of early production versions of the aircraft.

Production

Production of the I-16 began at zavod 39, the factory attached to the TsKB design bureau. This plant was not suitable for the large scale manufacture of series aircraft, and large scale production began at zavod 21 at Gor'ky. Later on large scale production also began at zavod 153 in Novosibirsk. Zavod 21 produced 8,494 aircraft, Zavod 153 produced 1,307, and Zavod 458 another 439, all two-seat trainers.

Zavod 39 was responsible for the first fifty production aircraft, built in 1934 and powered by M-22 engines. After that it only built eight more I-16s - four in 1935 and four in 1936. Of these five were lightened aircraft used by the 'Red Five' aerobatic team and powered by imported Wright Cyclone R-1820F-3 engines (one of which was also used as the prototype for the I-16 tip 5.

Zavod 21 began production with the I-16 tip 4 (type 4), indicating that this was the fourth type of aircraft to be produced at the factory (including the Polikarpov I-5 and the Neman KhAI-1 passenger aircraft, the third earlier type eludes me). The fifty aircraft produced at Zavod 39 are sometimes referred to as the tip 1.

The I-16 was produced in impressively large numbers. Over 1,000 aircraft were built in every year from 1937 to 1941, with a peak of 2,710 in 1940. Production dropped away dramatically in 1942, when the last 83 aircraft, all two-seat trainers, were built at zavod 458.

Variants

I-16 tip 4

Full scale series production of the I-16 began at Zavod 21 with the M-22 powered tip 4. This aircraft was armed with two 7.62mm machine guns, mounted in the wings just outside the propeller disc. Around 400 tip 4s were built in 1934-35, before production moved onto the tip 5.

I-16 tip 5 (I-16 M-25A)

The I-16 tip 5 was the second mass-produced version of the aircraft. Early aircraft used imported Wright Cyclone R-1820F-3 engines, but most used licence built 730hp M-25A engines, produced at zavod 19. The tip 5 also had a stronger structure, an oxygen system and a better hand-cranking system for the undercarriage. Take-off weight increased, but so did top speed, reaching 283mph. The tip 5 remained in production from 1936 until 1939, although production tailed off dramatically after 1937, with 264 produced in 1938 and 53 in 1939,

The I-16 tip 5 saw active service during the Spanish Civil War, fighting on the Government side. It proved to be faster but less manoeuvrable than the German and Italian biplanes it faced, but was also found to be under-armed. It had been hoped that the increased rate of fire of the ShKAS machine guns (1,800rpm) would compensate for the limited number of guns (in contrast the I-4 was armed with four PV-1 guns with a rate of fire of 750rpm). Combat experience soon proved that this was not the case, and the tip 10 would carry twice as many guns.

I-16 tip 6

The tip 6 was powered by the 730hp M-25A engine, and saw the enclosed cockpit replaced by an open cockpit with windscreen. This was introduced partly because of pressure from the pilots, who preferred open cockpits, and partly because the material used for the cockpit cover tended to go opaque quite quickly. During the production run the OP-1 gun sight (identifiable by the long barrel protruding from the windscreen) was replaced by the PAK-1 gun site, with no barrel. Around 2,200 tip 5s and tip 6s were built, with perhaps one third of them being the tip 6.

I-16 tip 10 (I-16 M-25V)

The I-16 tip 10 was the first major production version to carry more than two guns. The two wing guns were retained, and were joined by two synchronised 7.62mm ShKAS machine guns mounted above the engine. It was given the 750hp M-25V engine, which was more effective at higher altitudes (although early aircraft were powered by the M-25A). It also featured pneumatically operated landing flaps, designed to reduce the landing speed. These proved to somewhat dangerous, with a habit of opening too quickly, and thus becoming air brakes, and by 1939 the flaps were mechanically operated.

I-16 tip 12 (I-16P - pushechnyy, cannon armed)

The I-16 tip 12 (or I-16P - pushhyechnyi or cannon armed) was the first version of the fighter to be armed with 20mm cannon. It was developed in 1936 by fitting two 20mm ShVAK cannon to a tip 5 airframe, with the cannon mounted in the wing centre section and synchronised to fire through the propeller arc. Only a small number of tip 12s were produced.

I-16 tip 17

The I-16 tip 17 was the first cannon armed version of the I-16 to be produced in significant numbers. This time the 20mm cannon were mounted further out, beyond the propeller arc. The type also retained the two machine guns in the upper fuselage. Despite the extra weight of the cannon the top speed of the I-16 only fell from 278mph on the tip 10 to 264mph on the tip 17. Twenty seven tip 17s were built in 1938, and 314 in 1939. Production them moved onto the tip 27.

I-16 tip 18

The I-16 tip 18 saw the introduction of a significantly more powerful engine, the Shvetsov M-62. This was a version of the M-25 with a two-speed supercharger, and was similar to the Wright Cyclone R-1820-G-5. The new engine provided 1,000hp at take-off and 800hp at 9,500ft and was only 103lb heavier than the M-25V. As a result the aircraft's top speed increased from 278mph at 10,367 to 288mph at 14,235ft, and the service ceiling and rate of climb also increased. The tip 18 was armed with four 7.62mm machine guns. The tip 18 entered production in 1939, when 177 were built. It was replaced during 1940 by the tip 24, which used an improved M-63 engine.

I-16 tip 20

The I-16 tip 20 was a version of the tip 18 that could carry 20.5 gallon auxiliary fuel tanks under the wings, extending its endurance by up to one hour. From January 1940 all new versions of the I-16 were able to carry the drop tanks.

I-16 tip 24

The I-16 tip 24 was the standard production version for 1940, and was also the faster version of the I-16. It was powered by the Shvetsov M-63, an improved version of the M-62 that provided 1,100hp at take-off and 900hp at 14,800ft. It also received a new spinner, propeller and a constant speed regulator. Its top speed rose to 303mph at 15,750ft, the only member of the I-16 family to break the 300mph barrier (although many production aircraft failed to reach their full potential). Like the tip 20 it could carry auxiliary fuel tanks under the wings.

I-16 tip 27

The I-16 tip 27 was the cannon-armed equivalent of the I-16 tip 20, and combined the airframe of the tip 18 with its two 20mm cannon in the wings with the ability to carry slipper-type auxiliary fuel tanks under the wings. Fifty nine were built in 1939, and a combined total of 277 tip 27s and 28s in 1940.

I-16 tip 28

The I-16 tip 28 combined the cannon armament of the tip 27 and the M-63 engine of the tip 24.

I-16 tip 29

The I-16 tip 29 was the final production version of the I-16, and was in production from 1940-1941. It saw a final change in armament. The wing guns were removed and a new Berezin 12.7mm UBS heavy machine gun was mounted below the fuselage. Racks capable of carrying three 82mm unguided rockets were mounted under both wings. The tip 29 retained the M-63 engine, although with a more suitable propeller. When carrying rockets it was the heaviest version of the family, and its top speed dropped to 266mph, although it could reach 292mph when not carrying external stores.

Two-seat Versions

UTI-2 tip 14

The first two-seat version of the I-16 was the UTI-2. Three prototypes were built, with dual controls and tandem individual enclosed cockpits. The type then entered production as the UTI tip 14. The enclosed canopy was replaced by a pair of windscreens, the engine starter and oxygen equipment were removed, but the retractable undercarriage remained. The UTI-2 was powered by the M-22 engine, but a shortage of these engines meant that only around 100 were built - 57 in 1935-36 and the rest in 1937.

UTI-3

The UTI-3 was a prototype for a UTI-2 with the M-58 engine, but the type wasn't put into production.

UTI-4 (tip 15)

The UTI-4 (tip 15) was the definitive version of the two-seat I-16 trainer. It was similar to the production UTI-2, with two tandem cockpits, each with its own windscreen. Like the UTI-2 it was unarmed, and lacked the engine starter and oxygen equipment. Some were also built with fixed undercarriage. Early production UTI-4s were powered by the M-25A while later aircraft got the M-25V. The UTI-4 remained in production from 1937 until 1942, and was the last version of the I-16 to be produced. Sources differ dramatically on the number produced, with estimates ranging from around 500 up to over 4,000!

As well as its use as a final trainer for the I-16, the UTI-4 was also used as a transition trainer for pilots about to move onto the Yak-1 and LaGG-3 fighters, and was also sometimes used as a reconnaissance aircraft after the German invasion of 1941.

Service Record

The I-16 began to appear in public during 1935. It took part in that year's May Day Parade, and in October one appeared at the Salone Internazionale Aeronautica in Milan. It rapidly became the most important fighter in the Red Air Force, which had 1,763 on strength on 1 October 1938 and 2,004 on 10 February 1939 (the I-15 and I-153 biplanes were present in almost the same numbers). By the start of the Second World War the figures had increased again, this time to 2256 machine gun armed aircraft and 245 cannon armed models, and one year later, in September 1940, the Red Air Force had over 4,000 I-16s of different types in service. The Navy possessed another 500 or so I-16s.

Spanish Civil War

The I-16 received its combat debut during the Spanish Civil War. In the summer of 1936 the Nationalist rebels began to receive modern aircraft from Germany and Italy, including Heinkel He 51 and Fiat CR.32 fighters. These aircraft quickly swept aside the small obsolete Spanish air force, and the democratic government was forced to call for foreign support. The Soviet Union responded by offering I-15 and I-16 fighters, Tupolev SB-2 bombers and the crews to fly them, although only in return for payment in gold.

I-15s arrived first, in late October 1936. The first I-16s arrived in November, and soon gained two nicknames. On the Republican side they became known as the 'moska', from the Russian for black fly. The Nationalists called the I-16 the 'rata' or rat, because of the new aircraft's impressive speed. This second nickname is the one that has stuck with the I-16.

The first sixteen I-16s were sent to Madrid, where they entered combat for the first time in mid-November. The first combat came on 13 November, and was the first action seen by both the I-16 aircraft and its pilots. Both sides lost two pilots during this first encounter, two in a collision between an I-16 and a He 51. Both sides tended to struggle to identify the various types of enemy aircraft at times, with the Nationalists calling the I-15 a 'Curtiss' and the I-16 a 'Boeing', while some early Soviet reports included encounters with Bf 109s before they reached Spain.

By February 1937 the Soviet pilots had come to terms with their I-16s, and in that month won a series of aerial battles. Their aircraft was less manoeuvrable than the Heinkel He 51 and Fiat Cr 32, but also faster and with a better rate of climb. Its main weakness was that it was badly under armed, with only two 7.62mm machine guns.

A second, and much larger, batch of I-16 tip 5s arrived in Spain early in 1937, but the build quality on these aircraft was so poor that they were described as 'sabotaged'! A number of Soviet pilots were killed in these aircraft, in several cases when the badly built wings collapsed in flight.

A slow but steady flow of better quality I-16s arrived during 1937, but not in large enough numbers to make up for losses. At the same time the Nationalist rebels were receiving larger numbers of German and Italian aircraft, including the first Bf 109Bs, nine of which took part in a major air battle around Madrid in July 1937. At this point the I-16 could still hold its own in quality terms, for the Bf 109B was vastly inferior to the Bf 109E of 1940, but the Republicans were increasingly outnumbered.

In the spring of 1938 the Soviets sent a small batch of 31 I-16 tip 10s, with the more powerful M-25V engine and four machine guns, but once again these aircraft suffered from a poor build quality, with a number of problems with the engines and the guns. On 21 May 1938, the month after the new batch of aircraft arrived, there were only 43 combat ready I-16s in Spain. This improved dramatically in August when 90 better quality I-16 tip 10s arrived, the last of 276 I-16s to be delivered to Spain. Of these aircraft 112 were lost in combat, 62 lost in accidents and thirteen lost in a variety of incidents. Direct Soviet involvement in the Civil War ended late in 1938, when all of the volunteer pilots were ordered to return home, and the war itself ended with a Nationalist victory on 1 April 1939. The I-16 had held its own against its original biplane opponents and against the Bf 109Bs, but ominously the I-16 was already close to its peak performance, while the Bf 109 was only at the very beginning of its development.

China

In August 1938 the Soviet Union signed a non-aggression pact with the Soviet Union, which included a number of secret clauses in which the Soviets promised to provide direct military assistance against the Japanese. In the next two years 216 I-16s (a mix of tip 5s and tip 10s) were provided to China, alongside 347 I-15s and around 100 I-153s. Once again the aircraft were accompanied by volunteer pilots.

The first batch of I-16s arrived in September 1936 and were split between Soviet volunteers and Chinese pilots. The difficult nature of the I-16 and the limited time available for training mean that few of the Chinese pilots were able to come to grips with the new fighter at first, and a large number were destroyed in accidents.

Over China the I-16 came up against the A5M2 Claude. Both sides appear to have believed that they had the better fighter (something still largely reflected in books on the two aircraft). As is so often the case both side's pilots over-claimed, giving both sides the impression that they were shooting down large numbers of enemy fighters for limited losses.

The A5M2 and the I-16 were quite closely matched. The A5M2 was 20mph slower than the I-16, but more manoeuvrable. Like the I-16 tip 5 it was armed with two machine guns (in this case 7.7mm guns), so was out-gunned by the four-gun tip 10.

Khalkhin Gol/ Nomohan Incident

The I-16 next saw combat on the border between Mongolia and Manchuria, during the Khlakhin Gol or Nomohan Incident of 11 May-15 September 1939. At the start of this undeclared war the Red Air Force has a small number of I-16 tip 5s in the Far East, and these were rather outclassed by the Japanese Nakajima Ki-27 Army Type 97 Fighter. The situation changed as both sides flooded reinforcements into the area.

The Soviets eventually deployed 311 I-16s to the area, mainly the more heavily armed tip 10s and tip 17s. With a larger number of more modern aircraft and more experienced pilots the Red Air Force recovered from its poor start, and by the end of the fighting both sides had lost around 200 aircraft.

Perhaps the most notable incident of the air war over Manchuria was the use of unguided rockets as an air-to-air weapon for the first time. Thirteen victories were claimed for the rockets before the fighting came to an end.

Winter War

The I-16 was used extensively in the Winter War against Finland (1939-49). Exact details of the I-16s role in the fighting are unclear, but the Finns admitted to 48 losses in return for 207 victories, while the Soviets actually lost 261 aircraft - presumably many of these were accidental loses.

Second World War

The Soviet Union entered the Second World War in 1939 as an ally of Nazi Germany, taking part in the invasion and dismemberment of Poland. I-16 equipped fighter units were involved in the Soviet invasion of eastern Poland, but the Soviets had delayed their invasion for long enough to make sure that just about every Polish aircraft was fighting the Germans, and there are no records of any clashes between Soviet and Polish fighters.

By 1941 the I-16 was slowly being replaced by the LaGG-3, MiG-3 and Yak-1 fighters, but it was still present in large numbers when the Germans invaded, representing around 40% of the fighter force, and 38% of the 4,226 fighters facing the German invasion. As with every type of Soviet aircraft vast numbers of I-16s were lost on the ground in the immediate assault, but after that it just about held its own, suffering a similar rate of losses to the more modern fighters that were replacing it.

I-16 pilots found themselves in roughly the same position as biplane pilots when faced with the Bf 109. The German fighter was faster but less manoeuvrable than the I-16, and so could choose when and where to fight. If the German pilot could be lured into a dogfight then the superior manoeuvrability of the I-16 would come into play, although the German could use his superior speed to escape combat. By early in 1942 the Red Air Force was recommending the head-on attack, something of an act of desperation given that by 1941 the Bf 109 was better armed than most I-16s (apart from the small number of cannon armed aircraft).

The I-16 was used in several roles during the first two years of fighting on the Eastern Front. The standard machine gun armed versions were used as fighter aircraft. When flown by an experienced pilot the more powerful I-16s could almost hold their own against the Bf 109E, but not against later versions of the aircraft. The I-16 saw most use early in the war, when Soviet fighter tactics (involving large numbers of fighters in tight formations) gave the Germans a massive advantage, so losses were inevitably heavy.

The Naval Air Arm also used the I-16 against the Germans, most famously during the siege of Leningrad, where they were used to protect transport aircraft bringing supplies into the beleaguered city. The naval fighters were also used during the defence of Odessa at the other end of the long front line.

The I-16 was of limited use against German bombers, as it was slower than the Ju 88 (as were many other fighter aircraft in service at the time), while its limited machine gun armament meant that the sturdy He 111 could often survive being attacked.

The cannon and 12.7mm armed versions of the I-16 were used as ground attack aircraft until enough Il-2s were available to replace them. The aircraft could also carry six unguided rockets, which gave it quite a powerful punch in this role, but the I-16 was at best lightly armoured, and so losses were high.

Although the Red Air Force lost huge numbers of I-16s, the Luftwaffe also suffered heavy casualties in the early part of the fighting, many of them inflicted by pilots flying the I-16.

The I-16 quickly faded from the front line. Production of the single seat fighter stopped in 1941, and so losses could only be replaced until stocks ran down. By the end of 1941 the number of I-16s with units on the front had dropped from just over 1,600 at the time of the German invasion to only 240, and by 1 July 1943 only 42 were still in operational use. The I-16 remained in use with units away from the front line for a little longer, but only 42 were still in use in the western part of the Soviet Union at the end of 1943 and in 1944 the aircraft was withdrawn in the west. They remained in use in the east almost to the end of the war, and the 888th IAP operated the type until August 1945, but none were used during the brief but effective Soviet invasion of Manchuria in the last few days of the war against Japan.